djfrostsf Posted May 23, 2013 Share Posted May 23, 2013 Hey Guys, I searched for an FAQ but came up with no matches. Im just curious what the difference in down pipes is. Separated wastegate vs bell mouth. Is there a downside to bellmouth design? Link to comment Share on other sites More sharing options...
DeltaNu1142 Posted May 23, 2013 Share Posted May 23, 2013 Man, I've been wondering when someone would finally post a thread about downpipes. Tits mcgee Link to comment Share on other sites More sharing options...
compression Posted May 23, 2013 Share Posted May 23, 2013 When the exhaust comes out of the turbocharger it comes out through the turbine wheel (spinning it in the process) and into the downpipe. However, since these turbos have internal wastegates (exhaust bypass) the wastegate port also outlets into the downpipe. With a Bellmouth DP, both the main flow out of the turbine and the wastegate bypass dump into one larger chamber, like this: http://spun-autosports.com/catalog/images/SUBARU_Invida_Version_2_Polished_Downpipe.jpg The alternative is to keep the wastegate bypass flow separate (divorced) from the main flow out of the turbine for a bit before merging them back together. Like this: http://spun-autosports.com/catalog/images/633360826897165071_0.jpg So, now which one is better? Is it a good thing to keep the flows divorced? This is where all the armchair engineers pipe-up with theories and speculations. Maybe there is even some actual data on the web somewhere too. Personally, I dont think it really matters either way, because both are light-years better than stock. Link to comment Share on other sites More sharing options...
Xplosivo1 Posted May 23, 2013 Share Posted May 23, 2013 When the exhaust comes out of the turbocharger it comes out through the turbine wheel (spinning it in the process) and into the downpipe. However, since these turbos have internal wastegates (exhaust bypass) the wastegate port also outlets into the downpipe. With a Bellmouth DP, both the main flow out of the turbine and the wastegate bypass dump into one larger chamber, like this: http://spun-autosports.com/catalog/images/SUBARU_Invida_Version_2_Polished_Downpipe.jpg The alternative is to keep the wastegate bypass flow separate (divorced) from the main flow out of the turbine for a bit before merging them back together. Like this: http://spun-autosports.com/catalog/images/633360826897165071_0.jpg So, now which one is better? Is it a good thing to keep the flows divorced? This is where all the armchair engineers pipe-up with theories and speculations. Maybe there is even some actual data on the web somewhere too. Personally, I dont think it really matters either way, because both are light-years better than stock. Is that really your first post? Informative and helpful, thanks! To add to it, I believe the wastegate dump on the stock pipe is just a wall with a slight angle. Link to comment Share on other sites More sharing options...
compression Posted May 23, 2013 Share Posted May 23, 2013 Stock is a terrible design, it basically dumps the wastegate output right into a wall. Very cost efficient though....sometimes the accountants win in design decisions. Yes my first post on here. Not new to cars or subaru's though. Link to comment Share on other sites More sharing options...
rob-2 Posted May 23, 2013 Share Posted May 23, 2013 When the exhaust comes out of the turbocharger it comes out through the turbine wheel (spinning it in the process) and into the downpipe. However, since these turbos have internal wastegates (exhaust bypass) the wastegate port also outlets into the downpipe. With a Bellmouth DP, both the main flow out of the turbine and the wastegate bypass dump into one larger chamber, like this: http://spun-autosports.com/catalog/images/SUBARU_Invida_Version_2_Polished_Downpipe.jpg The alternative is to keep the wastegate bypass flow separate (divorced) from the main flow out of the turbine for a bit before merging them back together. Like this: http://spun-autosports.com/catalog/images/633360826897165071_0.jpg So, now which one is better? Is it a good thing to keep the flows divorced? This is where all the armchair engineers pipe-up with theories and speculations. Maybe there is even some actual data on the web somewhere too. Personally, I dont think it really matters either way, because both are light-years better than stock. Agreed. I think whichever is cheaper is probably best. I picked up an Invidia for $291 from rallysports. Link to comment Share on other sites More sharing options...
AZP Installs Posted May 24, 2013 Share Posted May 24, 2013 Great post and explanation. I would also add a few other items as well... Stay away from the cheapo knockoff brands of downpipes. We've been in this business for 13 years and we see a lot of cars come through our shop. The best brands we've seen in terms of fit and finish and consistently having proper specs to bolt up are the Invidia and Cobb. Almost all the other ones have close to a 50% chance of not fitting properly without having to tweak it or manhandle it or mangle it. Additionally unless you are going for BIG power, a catted aftermarket DP will yield almost the same results and you won't have to worry about your state emissions laws. -Mike Paisan AZP's First Private Track Event, June 19 at NJMP Thunderbolt $315 including Classroom and Mentor! http://www.pbase.com/paisan/image/91072632.jpg http://www.pbase.com/paisan/image/145749898/original.jpg http://www.pbase.com/paisan/image/133406601.jpg http://www.whiteline.com.au/images/logos/perf1.jpg 11+ Years Maintaining, Modifying and Educating TriState Subaru Enthusiasts. Call directly as We carry almost every manufacturer now, so before you buy parts call us. Like us on Facebook! | E-mail: sales@azpinstalls.com | 725 Fairfield Ave | Kenilworth, NJ 07033 | 908.248.AZP1 (2971) | T-1 Certified Amsoil Direct Jobber |AIM: AZP Installs "Race Tested, Enthusiast Approved!" Link to comment Share on other sites More sharing options...
AZP Installs Posted May 24, 2013 Share Posted May 24, 2013 Lastly, the 05-09 LGT Automatics do not use the same Downpipe as the Manual 05-09 LGT and 08+ WRX, so make sure to take that into account when purchasing. -Mike Paisan AZP's First Private Track Event, June 19 at NJMP Thunderbolt $315 including Classroom and Mentor! http://www.pbase.com/paisan/image/91072632.jpg http://www.pbase.com/paisan/image/145749898/original.jpg http://www.pbase.com/paisan/image/133406601.jpg http://www.whiteline.com.au/images/logos/perf1.jpg 11+ Years Maintaining, Modifying and Educating TriState Subaru Enthusiasts. Call directly as We carry almost every manufacturer now, so before you buy parts call us. Like us on Facebook! | E-mail: sales@azpinstalls.com | 725 Fairfield Ave | Kenilworth, NJ 07033 | 908.248.AZP1 (2971) | T-1 Certified Amsoil Direct Jobber |AIM: AZP Installs "Race Tested, Enthusiast Approved!" Link to comment Share on other sites More sharing options...
gear_monkey Posted May 25, 2013 Share Posted May 25, 2013 Lastly, the 05-09 LGT Automatics do not use the same Downpipe as the Manual 05-09 LGT and 08+ WRX, so make sure to take that into account when purchasing. -Mike Paisan AZP's First Private Track Event, June 19 at NJMP Thunderbolt $315 including Classroom and Mentor! http://www.pbase.com/paisan/image/91072632.jpg http://www.pbase.com/paisan/image/145749898/original.jpg http://www.pbase.com/paisan/image/133406601.jpg http://www.whiteline.com.au/images/logos/perf1.jpg 11+ Years Maintaining, Modifying and Educating TriState Subaru Enthusiasts. Call directly as We carry almost every manufacturer now, so before you buy parts call us. Like us on Facebook! | E-mail: sales@azpinstalls.com | 725 Fairfield Ave | Kenilworth, NJ 07033 | 908.248.AZP1 (2971) | T-1 Certified Amsoil Direct Jobber |AIM: AZP Installs "Race Tested, Enthusiast Approved!" Pure wisdom here! I had a tuner sell me and install a Perrin dp for my 5eat that was made for a mt. It rubbed the firewall and auto tranny pan. Horrible noise inside the cabin. When I went to the Invidia, it was night and day improvement. Link to comment Share on other sites More sharing options...
AZP Installs Posted May 25, 2013 Share Posted May 25, 2013 Pure wisdom here! I had a tuner sell me and install a Perrin dp for my 5eat that was made for a mt. It rubbed the firewall and auto tranny pan. Horrible noise inside the cabin. When I went to the Invidia, it was night and day improvement. We've seen it and fixed it many times in the past. -Mike Paisan AZP's First Private Track Event, June 19 at NJMP Thunderbolt $315 including Classroom and Mentor! http://www.pbase.com/paisan/image/91072632.jpg http://www.pbase.com/paisan/image/145749898/original.jpg http://www.pbase.com/paisan/image/133406601.jpg http://www.whiteline.com.au/images/logos/perf1.jpg 11+ Years Maintaining, Modifying and Educating TriState Subaru Enthusiasts. Call directly as We carry almost every manufacturer now, so before you buy parts call us. Like us on Facebook! | E-mail: sales@azpinstalls.com | 725 Fairfield Ave | Kenilworth, NJ 07033 | 908.248.AZP1 (2971) | T-1 Certified Amsoil Direct Jobber |AIM: AZP Installs "Race Tested, Enthusiast Approved!" Link to comment Share on other sites More sharing options...
phesa1005 Posted June 3, 2013 Share Posted June 3, 2013 Would a o8+ wrx down pipe,up pipe,top mount fit a 05 legacy gt automatic ? Link to comment Share on other sites More sharing options...
AZP Installs Posted June 3, 2013 Share Posted June 3, 2013 Would a o8+ wrx down pipe,up pipe,top mount fit a 05 legacy gt automatic ? The up would work. DP definitely not. TMIC probably but not 100% sure. Mike Link to comment Share on other sites More sharing options...
Moderators BarManBean Posted June 3, 2013 Moderators Share Posted June 3, 2013 ^^Mike is right--UP is fine, DP definitely not, and TMIC will fit. An downpipe designed for a 5EAT will fit a 5MT (with modification to the transmission bracket), but not the other way around. *hint hint* I have an Invidia downpipe for sale that will fit your car "Bullet-proof" your OEM TMIC! <<Buy your kit here>> Not currently in stock Link to comment Share on other sites More sharing options...
Moddiction Posted June 3, 2013 Share Posted June 3, 2013 I bought the CNT catted downpipe. Fitment and quality was great! WWW.MODDICTION.COM Moddiction Stainless steel and Titanium shift knobs. Drivetrain, suspension, brakes, exhaust, cooling, fuel, gauges+MUCH more! Link to comment Share on other sites More sharing options...
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